As a production (synthesis) method of nucleic acids such as DNA, RNA and the like, for example, a phosphoramidite method and the like are used. As a starting material for the nucleic acid synthesis by the phosphoramidite method, phosphoramidite of nucleoside (hereinafter to be simply referred to as “phosphoramidite”) is used. Examples of the protecting group at the 2′-position of the aforementioned phosphoramidite include many protecting groups such as TBDMS (tert-butyldimethylsilyl) group, TOM (triisopropylsilyloxymethyl) group, ACE (bis(2-acetoxyethoxy)methyl) group and the like. As for TOM amidite, it is described in, for example, the following non-patent document 1 and the like.